Field of the Invention
The present invention relates to a method for carrying out recombination at a target locus. The method also relates to cell prepared according to a method of the invention which is carried out in vivo.
Description of Related Art
Different cell types may be used for different industrial purposes. For example: mammalian cell lines are used for antibody production; fungal cells are preferred organisms for production of polypeptides and secondary metabolites; bacterial cells are preferred for small metabolite and antibiotic production; and plant cells are preferred for taste and flavor compounds.
Recombinant techniques are widely employed for optimization of the productivity of such cells and/or the processes in which they are used. This can involve a multitude of options, including, but not limited to over expression of a gene of interest, deletion or inactivation of competing pathways, changing compartmentalization of enzymes, increasing protein or metabolite secretion, increasing organelle content and the like.
In the case of filamentous fungi, the limited availability of selectable markers complicates the construction of new cell lines. Typically, target sequences are altered in vitro to create mutant alleles with inserted antibiotic resistance markers. However, regulatory authorities in most countries object to the use of antibiotic resistance markers in view of the potential risks of spreading resistance genes to the biosphere from large-scale use of production strains carrying such genes. In addition, there is a limited number of selectable markers suitable for use in filamentous fungi.
Accordingly, selectable marker genes may need to be removed so that production strains may be used commercially and/or so that the same marker gene may be recycled for use in sequential strain modification.